Three-dimensional (3-D) images of internal organs are useful in many catheter-based diagnostic and therapeutic applications, and real-time imaging is widely used during surgical procedures. Ultrasound imaging is a relatively convenient mode of real-time imaging, though the resolution of real-time ultrasound images is generally not as good as the resolution obtained from other imaging modalities, such as computerized tomography (CT) and magnetic resonance imaging (MRI).
U.S. Pat. No. 6,106,466 to Sheehan, et al., whose disclosure is incorporated herein by reference, describes a method for generating a 3-D model of a heart from 2-D ultrasound images. Anatomical locations are manually identified in the 2-D images. A 3-D mesh serves as an archetypal heart shape, which is aligned with the anatomical locations so as to delineate the 3-D model.
Methods for segmenting 3-D structures by tissue type are known in the art. U.S. Pat. No. 4,751,643 to Lorensen, et al., whose disclosure is incorporated herein by reference, describes a method for determining how slices of a structure are connected across 2-D images. An operator specifies a threshold of intensity that identifies a tissue type to be displayed. The operator also selects an initial voxel, or seed, identifying the location of the structure. U.S. Pat. No. 5,187,658 to Cline, et al., whose disclosure is incorporated herein by reference, describes a method for segmenting internal structures by constructing a statistical probability distribution based on relative intensities of tissues as they appear in a 3-D image.
U.S. Pat. No. 5,903,664 to Hartley, et al., whose disclosure is incorporated herein by reference, describes a method for segmentation based on selecting a seed point within a region of interest (ROI), such as the left ventricle. The seed point is expanded to include points within the ROI that have the same classification as the seed point, based on a threshold value.
U.S. Patent Application Publication 2006/0253024 to Altmann, et al., whose disclosure is incorporated herein by reference, describes a method in which an operator marks contours-of-interest in one or more ultrasound images. A 3D model of the anatomical structure is constructed based on the contours of interest and on measured location and orientation coordinates of the ultrasonic sensor.
U.S. Patent Application Publication 2007/0049817 to Preiss, et al., whose disclosure is incorporated herein by reference, describes a method for registering 3-D images with cardiac maps that comprise discrete points. The registration is performed by identifying sites of functional or physiological information, such as scar tissue, while acquiring points in the cardiac map. The sites are manually identified in the 3-D image, and the map and the 3-D image are registered according to the identified sites common to the two.
U.S. Patent Application Publication 2007/0106146 to Altmann, et al., whose disclosure is incorporated herein by reference, discloses a method and system for synchronizing the acquisition of an electro-anatomical map and a 3-D ultrasound image and subsequently displaying overlaid, cyclical motion of the two.
U.S. Patent Application Publication 2002/0049375 to Strommer describes a method for displaying an image sequence of a cyclically moving organ. An organ timing signal is detected, and a plurality of two-dimensional images of the organ are acquired from different locations and orientations using an image detector. Each of the two-dimensional images is associated with its corresponding image detector location and orientation and with a reading of the organ timing signal. The two-dimensional images are grouped according to cycle points in the organ motion cycle, and each group is used in reconstructing a three-dimensional image associated with the respective cycle point.
Methods for 3-D mapping of a heart using a position-sensing catheter are well known in the art. For example, U.S. Pat. No. 5,738,096 to Ben-Haim, whose disclosure is incorporated herein by reference, describes a position-sensing probe brought into contact with multiple points in the body so as to generate an anatomical map. Physiological properties, including electrical activity on the surface of the heart, may also be acquired by the catheter. (Generation of such an electro-anatomical map may be performed with a CARTO™ navigation and mapping system, manufactured and sold by Biosense Webster, Inc., of Diamond Bar, Calif.)
U.S. Pat. No. 6,226,542 to Reisfeld, whose disclosure is incorporated herein by reference, describes a method for generating a 3-D model based on a cardiac map. An arbitrary, closed 3D curved surface is roughly adjusted to a shape which resembles a reconstruction of the points of the map. Thereafter, a flexible matching stage is performed to bring the closed surface to accurately resemble the shape of the actual volume being reconstructed.
Some medical imaging systems apply methods for registering multiple 3-D models. For example, U.S. Pat. No. 5,568,384 to Robb, et al., whose disclosure is incorporated herein by reference, describes a method for synthesizing multiple 3-D image sets into a single composite image. A transformation of one image is performed to align it with a second image. U.S. Pat. No. 6,556,695, issued to Packer, et al., whose disclosure is incorporated herein by reference, suggests that a magnetic resonance image can be acquired, and then registered with a subsequently acquired electrical activation map or ultrasound image.
An ultrasound catheter may be used for imaging of the endocardium (i.e., the inner surfaces of the heart). For example, U.S. Pat. No. 6,716,166 to Govari and U.S. Pat. No. 6,773,402 to Govari, et al., whose disclosures are incorporated herein by reference, describe systems for reconstructing body cavities from two dimensional (2-D) images obtained with an ultrasound catheter. The catheter may also comprise position sensors, which determine coordinates of the catheter within a body cavity. Acoustic transducers in the catheter emit ultrasonic waves that are reflected from a surface of the cavity. The distance from each of the transducers to the surface is determined, and the distance measurements and the catheter position are combined so as to reconstruct the three-dimensional (3-D) shape of the cavity.
A report by McInerney and Terzopoulos, appearing in “Deformable Models in Medical Image Analysis: A Survey,” Medical Image Analysis (1:2), June 1996, pages 91-108, which is incorporated herein by reference, describes a computer-assisted medical image analysis technique for segmenting, matching, and tracking anatomical structures by exploiting (bottom-up) constraints derived from the image data together with (top-down) a priori knowledge about the location, size, and shape of these structures.
Another analysis technique is described by Neubauer and Wegenkittl in “Analysis of Four-Dimensional Cardiac Data Sets Using Skeleton-Based Segmentation,” the 11th International Conference in Central Europe on Computer Graphics, Visualization and Computer Vision, University of West Bohemia, Plzen, Czech Republic, February 2003, which is incorporated herein by reference. The authors describe a computer-aided method for segmenting parts of the heart from a sequence of cardiac CT (Computerized Tomography) images, taken at a number of time points over the cardiac cycle.